1. Technical Field
The present invention relates to an apparatus and a method for supplying a hydrogen gas and to a quartz glass manufacturing apparatus.
2. Description of the Related Art
It is known to manufacture optical fiber base materials by using Vapor Phase Axial Deposition (VAD) method and Outside Vapor Deposition (OVD) method. Either method includes a step of generating and depositing silicon dioxide (SiO2) through hydrolysis of a silicon compound such as silicon tetrachloride (SiCl4) by means of an oxyhydrogen flame. Therefore, the above optical fiber base material manufacturing methods require continuous supply of a hydrogen gas.
A hydrogen gas for industrial use may be preserved in the liquid state for the purpose of reducing hydrogen embrittlement of the tank used for the preservation. Therefore, there is hydrogen supply equipment that heats and evaporates liquid hydrogen preserved in a low-temperature storage and supplies a resulting hydrogen gas.
The hydrogen gas used for manufacturing optical fiber base materials may be manufactured or preserved at ordinary temperatures, or may originate from liquid hydrogen preserved in the above-mentioned manner. Thus, there is also equipment that can switch the hydrogen gas supply source, for example, that uses a hydrogen gas manufactured and supplied at ordinary temperatures while temporarily using a hydrogen gas originating from liquid hydrogen.
Here, a hydrogen gas contains isomers, one of which is ortho-hydrogen and the other is para-hydrogen. The ortho-hydrogen and the para-hydrogen are in equilibrium at different content ratios between the isomers depending on the temperature of the hydrogen gas. Therefore, the content ratio between the ortho-hydrogen and the para-hydrogen differs between the hydrogen that is preserved at a low temperature in the liquid state and the hydrogen that is manufactured at ordinary temperatures.
In addition, the ortho-hydrogen and the para-hydrogen have different properties from each other. For example, there is a difference of approximately 6% in the constant pressure specific heat at 0 degrees Celsius. Therefore, a thermal type mass flow meter, which is frequently used as a hydrogen gas flow meter, indicates different measured values for same the flow rate between the ortho-hydrogen and the para-hydrogen, for example.
Japanese Patent Application Publication No. 2006-009917 discloses that a magnetic field may be applied to liquid hydrogen to prevent ortho-hydrogen from transforming into para-hydrogen. Japanese Patent Application No. 2008-187924 discloses a technique of calculating a factor for compensating a measured value of the flow rate of a hydrogen gas depending on the origin of the hydrogen gas, by obtaining in advance a measured value for the flow rate of a hydrogen gas originating from liquid hydrogen and a measured value for the flow rate of a hydrogen gas at ordinary temperatures.
However, the method based on the modification of a hydrogen gas through application of a magnetic field is only effective if the magnetic field is applied to all of the parts including the transport equipment and the supply equipment, in addition to the low-temperature storage. The method based on the calculation of the compensation factor is effective only when the hydrogen gas flowing through the mass flow meter is known to be one of the two types of hydrogen gases.